Abstract As individuals with type 2 diabetes (T2D) live into older age, patterns of care established during middle age need to be adjusted in response to age-related changes in physiology and life circumstances. Advance care planning (ACP) is a critical tool for supporting older adults to participate with clinicians in making real-time, complex medical decisions over the course of serious illness so that the medical care they receive is aligned with their goals. Although often applied to end-of-life decisions (e.g. advanced directives regarding life- sustaining treatments), the ACP paradigm has been expanded to also prepare patients to more effectively participate in re-assessing current treatment goals for long-term chronic conditions such as T2D. The goal of this study is to apply the expanded ACP paradigm (skill building and preparation for values elicitation, decision- making, and communication) to the specific clinical problem of hypoglycemia-related adverse outcomes in vulnerable older patients with T2D. We will adapt our existing, evidenced-based patient-facing, online PREPARE tool (prepareforyourcare.org) to address treatment intensity in older adults with T2D at increased risk for hypoglycemic events (i.e. prescribed insulin or sulfonylureas) (Aim 1). We will then conduct a randomized clinical trial in the primary care setting comparing this new ACP-T2D tool to usual care among 600 adults ? 75 years of age and at increased risk for hypoglycemic events (Aim 2). The goal of this intervention is to enable informed, prepared patients to engage with their primary care providers in re-assessing their diabetes treatment intensity and treatment goals in the context of ACP. We hypothesize that for many of these high-risk older adults, these informed conversations will lead to medication de-prescribing and corresponding lower incidence of clinically-significant hypoglycemia (primary clinical outcome, defined by the American Diabetes Association as hypoglycemia requiring resuscitative help from another person) relative to usual care. We will also examine prescription changes, ED/hospital admissions, and a set of patient-reported outcomes related to communication, diabetes management, and ACP. In Aim 3 we will analyze heterogeneity of treatment effect by clinical and patient-level contextual factors to inform future iterations of this expanded ACP paradigm. If successful, this relatively low-cost and generalizable framework could be scaled and applied in a wide variety of healthcare settings and to a range of chronic conditions in which evolving risks, benefits, and consequences of treatment require re-assessment with age.